Patient specific instrumentation (PSI) for orthopedic surgery and systems and methods for using X-rays to produce same

ABSTRACT

A method of creating a patient specific instrument (PSI) for use in knee replacement surgery is described which includes performing at least two two-dimensional X-ray scans of a bone, each of the X-ray scans being taken from different angular positions, generating a digital bone model of the bone based on the X-ray scans, planning the PSI based on the digital bone model, including determining locations for one or more anchor points on the PSI which are adapted to abut a surface of the bone, the determined locations of the anchor points being disposed on the PSI at locations corresponding to areas of expected high accuracy on the digital bone model generated by the X-ray scans. The areas of expected high accuracy include at least a peripheral bone contour in at least one of the angular position of the X-ray scans. A suite of such PSI instruments is also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 14/496,924 filed Sep. 25, 2014, which claims priority on U.S. PatentApplication No. 61/882,410 filed Sep. 25, 2013, the entire content ofeach of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to patient specificinstrumentation (PSI) used in orthopedic surgical applications, and moreparticularly to PSI devices and/or implants which are created based onpatient specific bone models produced from X-rays.

BACKGROUND

Improvements in the design, creation and use of patient specificinstrumentation and/or implants (PSI) continue to be sought. PSI devicesare purpose designed to suit a specific patient's anatomy. In thecontext of orthopedic surgical applications, this is most commonlyaccomplished by first generating a digitized bone model of the specificpatient's bone based on images produced from a Magnetic ResonanceImaging (MRI) scan of the patient's anatomy. MRI scans are most oftenused because they offer precise imaging of the anatomical features ofthe patient, including bone, cartilage and other soft tissue, whichenables the creation of an accurate patient-specific digitized bonemodel. This bone model can then be used to create PSI devices.

SUMMARY OF THE INVENTION

In accordance with one aspect, there is accordingly provided a patientspecific instrument for positioning a surgical guide on a bone duringknee replacement surgery, the patient specific instrument being formedbased on a digital bone model generated using at least twotwo-dimensional X-ray scans taken from different angular positions, thepatient specific instrument comprising: a body having fastener guideholes, the fastener guide holes adapted to receive fasteners thereinused to fasten the surgical guide to the bone; and one or more anchorelements on the body adapted to abut one or more surfaces of the bone,the anchor elements being disposed in locations on the body of thepatient specific instrument overlying a peripheral bone contour of thebone in at least one of the two-dimensional X-ray scans, said locationsand the peripheral bone contour corresponding to areas of expected highaccuracy on the digital bone model generated by the two-dimensionalX-ray scans.

In accordance with another aspect, there is also provided a method ofpositioning fasteners for mounting a resection cutting block on a boneduring orthopedic knee replacement surgery, including: obtaining atleast two two-dimensional X-ray scans of the bone taken from differentangular positions, and a digital bone mode of the bone based on saidtwo-dimensional X-ray scans; using a patient specific instrumentdesigned based on the digital bone model, the patient specificinstrument having one or more anchor points thereon which are adapted toabut a surface of the bone, the anchor points being disposed on thepatient specific instrument at locations corresponding to areas ofexpected high accuracy on the digital bone model generated by thetwo-dimensional X-ray scans, said areas of expected high accuracyincluding at least a peripheral bone contour in at least one of saidangular positions; and engaging the patient specific instrument to thebone by abutting the anchor points against the bone; angularly adjustingthe patient specific instrument in at least one of varus-valgus,flexion-extension, and rotation, in order to position the patientspecific instrument in a predetermined position and orientation; andinserting the bone pins through corresponding pin holes extending the abody of the patient specific instrument.

There is alternately provided a method of creating a patient specificinstrument for use in knee replacement surgery, the method comprising:performing at least two X-ray scans of one or more bones, each of theX-ray scans being taken from different angular positions; generating adigital bone model of said one or more bones based solely on the X-rayscans; planning the patient specific instrument based on the digitalbone model, including determining locations for one or more anchorpoints on the patient specific instrument which are adapted to abut asurface of said one or more bones, the determined locations of the oneor more anchor points being disposed on the patient specific instrumentcorresponding to areas of expected high accuracy on the digital bonemodel generated by the X-ray scans, said areas of expected high accuracyincluding at least a peripheral bone contour in at least one of saidangular positions; and producing the patient specific instrument havingsaid one or more anchor points thereon.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating a method for forming patient specificinstrumentation (PSI) for use in performing total knee replacement (TKR)surgery, in accordance with the present disclosure.

FIG. 2 is front perspective view of a PSI tibial pin guide, producedbased on X-rays of the tibia and for use in performing tibial resectionduring a TKR surgery.

FIG. 3 is a rear perspective view of the PSI tibial pin guide of FIG. 2.

FIG. 4 is a front perspective view of a PSI tibial resection cut guidefor use in conjunction with the PSI tibial pin guide of FIG. 2.

FIG. 5 is a top perspective view of a Flexion-Extension alignment bootused in conjunction with the PSI tibial pin guide of FIG. 2.

FIG. 6 is a perspective view of a PSI tibial pin guide jig in accordancewith an alternate embodiment of the present disclosure.

FIG. 7 is a perspective view of a PSI tibial extra-medullary guide inaccordance with an embodiment of the present disclosure.

FIG. 8 is a partial perspective view of a proximal portion of the PSItibial extra-medullary guide of FIG. 7.

FIG. 9 is a perspective view of a tibia mounted PSI hip knee angle (HKA)instrument having a malleoli clamp, in accordance with an embodiment ofthe present disclosure.

FIG. 10 is a partial perspective view of a proximal portion of the PSIHKA instrument of FIG. 9.

FIG. 11 is a schematic side elevation view of a leg alignment jig foruse within the X-ray produced PSI tibial guides of the presentdisclosure, for use in performing TKR surgery.

FIG. 12 is a partial perspective view of a proximal portion of a hybridPSI tibial pin and extra-medullary guide in accordance with anotherembodiment of the present disclosure.

FIG. 13a is a distal end view of a PSI femoral pin guide, produced basedon X-rays of the femur and for use in performing femoral resectionduring a TKR surgery.

FIG. 13b is a partial perspective anterior-medial view of the PSIfemoral pin guide of FIG. 13 a.

FIG. 14 is a perspective view of a femoral resection cut guide for usein conjunction with the PSI femoral pin guide of FIGS. 13a -13 b.

FIG. 15a is a distal perspective view of a PSI anterior-posterior (A-P)sizer in accordance with one embodiment of the present disclosure.

FIG. 15b is a distal perspective view of a PSI A-P sizer in accordancewith an alternate embodiment of the present disclosure, shownpositioning a posterior cutting guide thereon.

FIG. 15c is a perspective view of an additional instrument for us inre-positioning the posterior cutting guide shown in FIG. 15 b.

FIG. 16 is a perspective view of a PSI femoral pin guide jig inaccordance with an alternate embodiment of the present disclosure.

DETAILED DESCRIPTION

Patient specific instrumentation/instruments/implants (collectively“PSI” as used herein) are purpose designed to suit a specific patient'sanatomy, based on a digitized bone model of the anatomy in question.Such PSI devices are most commonly created based on digital bone modelsthat are generated using Magnetic Resonance Imaging (MRI) images of thebone(s) and surrounding soft tissue (e.g. cartilage). MRI scans have todate been largely preferred for the creation of such PSI devices, due tothe fact that the MRI scan images are capable of depicting cartilage aswell as the bone, thereby ensuring the accuracy of the resulting surgeryperformed using the PSI device thus produced. However, such MRI scansare both costly and time consuming to conduct.

Accordingly, the present inventors have developed a suite of patientspecific surgical implements particularly adapted for use in conductingknee replacement surgery (such as total knee replacement (TKR)), whichare specifically designed to be created based on a digital bone modelgenerated only using X-rays taken of the patient's bone(s).

Thus, the presently described system and method enables the creation anduse of PSI components for knee surgery which are designed and createdusing a digital bone model generated using only two-dimensional (2D)X-ray images of the specific patient's bone(s). This enables the PSIcomponents described herein to be created quickly and in a more costeffective manner than with known prior art systems and methods, whichrequire the use of MRI scans to produce the digital bone models.

In accordance with a general aspect of the present disclosure,therefore, a patient specific digital bone model is first created usingonly X-ray scan images (i.e. no MRI scans are required), so as todigitally reconstruct the bone in a surgical planning computer programand/or a computer assisted surgery (CAS) system. At least two or moreX-ray images are required of the patient's bone or bones, which must betaken from different angular positions (e.g. one lateral X-ray and onefrontal or anterior X-ray). While one X-ray image may be insufficient,more than two X-ray images may alternately be used. Generally, thegreater the number of X-ray scans taken from different angular positions(e.g. lateral, medial, anterior, posterior, etc.), the greater theresulting accuracy of the digital bone model created therefrom. However,the desired accuracy has been found to be obtainable when only twoX-rays are taken from perpendicularly disposed angular positions (e.g.lateral and frontal/anterior).

Once a digital bone model is created using the surgical planningcomputer program and/or CAS system, using only the two or more X-rayimages of the bone(s) of the specific patient, a PSI surgical componentas described herein is then designed using the CAS system as will bedescribed, and then subsequently created specifically for the patient,using the digital bone model of the patient's anatomy created based onlyon the X-ray images. The PSI components as described herein maytherefore be created, once they have been planned/designed to fit withthe digital bone model, out of any suitable material, but these mayinclude plastics or metals which are suitable for use in surgicalapplications. Ideally, these PSI components are produced rapidly and onsite, using an additive manufacturing process such as 3-D printing.

While X-rays are typically perceived as being less precise than MRIimages, the present method and system can nevertheless be used to createPSI components which are specially adapted to be formed based on adigitized patient bone model generated using only X-ray images. Thus PSIdevices, tool and/or instruments described herein may accordingly bedesigned and created more time and cost effectively.

As will be seen, because an X-ray generated digital bone model is beingused, standard surgical tools, and even previously developed standardpatient-specific tools, cannot be readily used. This is because patientspecific tools developed based on MRI-generated bone models can bedesigned knowing precisely where any cartilage and other soft tissue islocated. As this is not the case for bone models generated using onlyX-rays images, any PSI component which is doing to be designed based onsuch X-ray bone models must be configured in such a way as to maximizethe accuracy of the component and more specifically its mounting pointswith the actual bone, in order to ensure that the end surgical resultwhen this component is used is acceptable.

The presently described PSI components, which are produced based solelyon X-ray generated digital bone models, therefore include one or moreanchor points thereon that are adapted to abut and/or otherwise engage asurface of the bone and that are disposed on the PSI component at one ormore locations corresponding to areas of expected high accuracy on thedigital bone model generated by the X-ray scans. These areas of expectedhigh accuracy on the digital bone model will generally correspond topoints on a peripheral bone contour in at least one of the angularpositions from which an X-ray image is taken. For example, if a frontal,or anterior, X-ray has been taken of the bone, the medial, lateral andproximal outer peripheral contours of the bone will be very accurate inthe X-ray image and thus in the resulting digital bone model createdthereby. As a result, points on the bone model which are disposed alongthese medial, lateral and/or proximal peripheral contours of the digitalbone model will be areas of expected high accuracy, even if the X-rayimage is not capable of revealing any cartilage present. Similarly, if alateral X-ray has been taken of the bone, the anterior, distal and/orproximal outer peripheral contours of the bone will be very accurate inthe X-ray image, and thus in the resulting digital bone model createdthereby. As a result, points on the bone model which are substantiallydisposed along these anterior, distal and proximal outer peripheralcontours of the digital bone model will be areas of expected highaccuracy, even if the X-ray image is not capable of revealing anycartilage present. Thus, by positioning any anchor or mounting elementsof a PSI component in locations on the PSI component which correspond tothese areas of expected high accuracy on the X-ray generated bone model,the PSI component so designed is particularly adapted for use withoutany appreciable loss in accuracy.

The term “anchor”, “anchor elements” or “anchor points” as used hereinis understood to mean points on the PSI component which engage the bonewhen the PSI component is mounted thereto, whether this be simply byabutting the bone without being directly fixed thereto (e.g. a bonespike, blade or jack screw which rests on the outer surface of the bone)or by being fastened (e.g. by a pin, bone screw, etc. which penetratesinto the bone for rigid fastening thereto). The term “anchor” as usedherein therefore does not necessarily imply rigid fastening bypenetration of the bone, but rather such anchors fix the PSI componentin place on the bone such that relative movement therebetween is notreadily possible.

Referring now to the Figures, these general aspects of the presentdisclosure as outlined above are described and depicted in greaterdetail with reference to an exemplary orthopedic knee surgery system,and more particularly with respect to performing a total kneereplacement (TKR) system involving components and methods specific toboth tibia and femur resection and prosthetic reconstruction.

This may include, for example, providing PSI tools and/or implants,formed in order to correspond with the patient specific digital bonemodel created based on X-ray images. This may further include digitizingthe tibial and/or femoral mechanical axis in order to be able to performthe TKR procedure on the patient using the PSI tools. This may be donein conjunction with a CAS system, for example one which employsinertial-based or micro-electro-mechanical sensor (MEMS) trackablemembers for use in orthopedic surgical applications. The presentlydescribed system, surgical tools and methods may therefore be used inconjunction with an inertial-based CAS system employing trackablemembers having inertial-based sensors, such as the MEMS-based system andmethod for tracking a reference frame disclosed in United States PatentApplication Publication No. US 2011/0218458, and the MEMS-based systemand method for planning/guiding alterations to a bone disclosed in U.S.Pat. Nos. 8,265,790 and 8,718,820, and in United States PatentApplication Publication No. 2009/0247863, the entire contents of each ofwhich is incorporated herein by reference. However, it is to beunderstood that the tools and methods described herein may also be usedwith other CAS systems. The present systems and methods may also be usedin conjunction with a tool for digitizing a mechanical axis of a tibiausing a CAS system, as described in U.S. Pat. No. 8,551,108, the entirecontent of which is incorporated herein by reference.

The PSI components of the present disclosure are all particularlyadapted for use during orthopedic knee surgery, such as TKR, and as suchthe surgical components of the present suite of surgical tools will nowbe described below generally as either tibial or femoral components,respectively adapted for use in the positioning of a resection cuttingguide on either the tibia or the femur, for the purposes of preparingthe bone for receipt of a prosthetic knee replacement implant. While theactual steps of the TKR surgery are as per those well known by thoseskilled in the art, the presently described PSI components differ inthat they are specifically adapted for use in a system and method whichhas produced the digital bone model using only X-ray images.

Tibial Components

In order to be able to resect a proximal end of the tibia T using aresection cutting guide 30, as shown in FIG. 4, locating pins 31 mustfirst be accurately positioned at the desired position and orientationrelative to the tibia T, such that the resulting resection cut will bemade at the correct position and angle to accept the planned prosthetictibial implant. Accordingly, several different embodiments will now bepresented, each of which can be used to position these locating pins 31.

In the embodiment of FIGS. 2-3, a PSI tibial pin guide 10 is shown whichis produced based on at least two X-rays of the tibia, taken from twodifferent angular positions as described above. The PSI tibial pin guide10 includes generally a body 12 including a distally extending portion15 and a pair of posteriorly extending arms 13. The distally extendingportion 15 of the body 12 has a slot 16 formed therein, which extendsfully through the distally extending portion 15 and is adapted toreceive therethrough an anterior bone pin 11. The slot 16 has atransverse width, in the medial-lateral (M-L) direction, substantiallysimilar although just slightly greater than the diameter of the anteriorpin 11. The slot 16 has a length, in the proximal-distal (P-D)direction, that is at least several times the diameter of the anteriorpin 11. As such, once the anterior pin is fastened in place in theanterior surface of the tibia T, the PSI tibial pin guide 10 can bemounted thereto by inserting the anterior pin 11 through the slot 16 inthe body 12 of the PSI tibial pin guide 10. Given the slot's length, thebody 12 of the PSI tibial pin guide 10 can therefore be slid in the P-Ddirection relative to the fixed anterior pin 11 as required. Althoughonly the anterior pin 11, and not the body 12 of the PSI tibial pinguide 10, is engaged to the bone, this pin-slot engagement neverthelesslocates, or constrains, the rotation of the PSI tibial pin guide 10(i.e. relative to longitudinal axis of the bone) while still permittingangular movement in the Varus-Valgus (V-V) and Flexion-Extension (F-E)orientations/directions.

At an upper end of the body 12 of the PSI tibial pin guide 10, the pairof posteriorly extending arms 13 each have a proximal anchor element 14disposed near the remote end thereof, the two proximal anchor elements14 comprising bone spikes or nails. These bone spikes 14 are adapted topenetrate any cartilage on the tibial plateaus P and engage, but notsubstantially penetrate, the underlying bone surface of the tibialplateau P. These proximal bone anchors 14 accordingly locate, orconstrain, the PSI tibial pin guide 10 in the V-V orientation relativethereto.

The remaining angular constraint required, and for which adjustment isprovided, for the PSI tibial pin guide 10 is in the F-E direction.Accordingly, the PSI tibial pin guide 10 includes an adjustment jackscrew 18 disposed at a remote end of the distally extending portion 15of the body 12, which has a bone abutting tip 20 thereon that formsanother anchor point or anchor element for abutting the tibia T. Byrotating the jack screw 18, the position of the body 12 of the PSItibial pin guide 10 relative to the tibia T can be adjusted in the F-Edirection/orientation.

Accordingly, the PSI tibial pin guide 10 includes one or more anchorelements disposed at different anchor points. In this case, at leastthree anchor elements are provided, namely the two bone spikes 14 whichabut medially-laterally opposite sides of the tibial plateau P and thedistally located jack screw 18. Importantly, each of these anchorelements is disposed at a location on the PSI tibial pin guide 10 whichcorresponds to, or more particularly overlies, point on the bone whichcorrespond to areas of expected high accuracy on the X-ray generatedbone model. More particularly, the two bone spikes 14 are locatedsubstantially along a proximal bone peripheral contour as defined in afrontal X-ray image taken of the tibia T, and the distal jack screw 18is located substantially along an anterior bone peripheral contour asdefined in a medial or a lateral X-ray image take of the tibia T.

The body 12 of the PSI tibial pin guide 10 also includes a pin guideelement 22 disposed at a distal end of a portion of the body adjacentthe distally extending portion 15. A pair of pin guide holes 24 extendthrough the pin guide element 22, and are configured to receivetherethrough the bone pins 31 which are used to mount the resectioncutting block 30 to the tibia (see FIG. 4).

The PSI tibial pin guide 10 also includes an optical positioning elementwhich is used to position the PSI tibial pin guide 10 in the desiredlocation relative to the tibia T. This optical positioning elementincludes a laser 26 which is engaged to a laser mount 27 disposed on anextension bar 25 protruding from the body 12 of the PSI tibial pin guide10. The laser 26 produces a laser beam B, which may be either a pointlaser beam or a planar beam as shown in FIG. 2. The laser 26 ispositioned such that its laser beam B projects onto the ankle and/orfoot of the patient. By aligning the laser beam B with either anatomicallandmarks on the foot (such as the malleoli of the ankle, for example)or other reference points or markings on another object substantiallyfixed relative to the ankle (such as the ankle boot 40 as shown in FIG.5, for example), the user can position the PSI tibial pin guide 10, andtherefore the pin guide holes 24 of the pin guide element 22 in apredetermined location which will result in the pins 31, when insertedthrough the pin guide holes 24 and fastened into the bone, to positionthe resection cutting block 30 mounted to these pins 31 in a selectedposition and orientation to perform the proximal resection cut of thetibia.

Referring more specifically to FIG. 5, the boot 40 may optionally beused in order to serve as a reference guide for aligning the PSI tibialpin guide 10 using the laser 26 as described above. More particularly,the boot 40 may include markings or other visually identifiabledemarcations, with which the laser beam B of the laser 26 can bealigned, thereby providing additional guidance to the user as thecorrect alignment of the laser, and thus the PSI tibial pin guide 10 towhich it is fixed, in the F-E direction.

Because the tibial pin guide 10 is a PSI component, it is designed andconfigured to tailor to the specific anatomical features of the tibia Tto which it is intended to be mounted. Therefore, while each tibial pinguide 10 will be slightly different to accommodate particularities ofeach patient's bone, they nevertheless include one or more anchor pointsthereon that are adapted to abut and/or otherwise engage a surface ofthe tibia T and that are disposed at one or more locations of the PSItibial pin guide 10 which correspond to areas of expected high accuracyon a digital bone model generated only by X-ray scans.

Referring now to FIG. 4 in more detail, a PSI tibial resection cut guide30 of the present system is shown which including a cutting block 32having a saw slot 37 extending therethrough and a base block 34 that isitself fastened in place on the tibia T using the cut guide pins 31. Thepins 31 are positioned and fixed in place as described above using thePSI tibial pin guide 10. The cutting block 32 is adjustable in one ormore directions relative to the base block 34, using a lockingadjustment mechanism 38. In the embodiment as shown in FIG. 4, thislocking adjustment mechanism 38 includes a stem 33 which forms part ofthe cutting block 32 and a mating opening in the base block 34 throughwhich the stem extends. A locking screw 35 is used to fix the base block34 to the stem 33 of the cutting block 33, such as to prevent relativemovement therebetween when the screw is tightened. As the stem 33 canslide within the opening in the base block, the cutting block 32 canaccordingly be displaced in a proximal-distal direction, in order toincrease or decrease the depth of the proximal resection cut asrequired. Accordingly, once the pins 31 are in place, the base block 34is slid onto the pins 31, whereupon the position of the cutting block 32relative to the fixed base block 34 can be adjusted as required. Oncethe predetermined position for the cutting guide slot 37, and thereforethe cutting block 32, is reached, the locking mechanism 38 is actuatedto fix the cutting block 32 in the appropriate position.

FIG. 6 shows a PSI tibial pin guide jig 40 in accordance with analternate embodiment of the present disclosure. This PSI jig 40 may bealternately used to align and position the mounting pins 31 for the PSItibial resection cut guide 30, however provides less adjustmentfeatures. The PSI tibial guide jig 40 is more akin to pin placement jigsused in conjunction with MRI-generated digital bone models. Nonetheless,however, the PSI tibia pin guide jig 40 is specifically designed to beused with digital bone model generated only using X-ray images.

Accordingly, the PSI jig 40 also includes one or more anchor elementsdisposed at different anchor points, which in this embodiment includestwo bone spikes 41 which abut medially-laterally opposite sides of thetibial plateau and an anterior abutting element 43 disposed on thedistally extending body 44. A pair of pin holes 45 also extend throughthe body 44, and are used as described above to position the pins 31used to mount the resection cutting block 30 to the tibia. Much as perthe PSI tibial pin guide 10 described above, each of the anchor elementsof the PSI jig 40 is disposed at a location on the PSI component whichcorresponds to, or more particularly overlies, a point on the bone whichis disposed in areas of expected high accuracy on the X-ray generateddigital bone model.

Referring now to FIGS. 7-8, an alternate PSI component of the presentlyproposed suite of surgical implements is shown, which could alternatelybe used instead of the PSI tibial pin guide 10 or the PSI jig 40. Inthis embodiment, a PSI tibial extra-medullary (E-M) guide 50 (or simply“PSI E-M guide”) is provided, which can be similarly used to accuratelyposition the pins 31 to be used to mount the resection cutting guide 30to the proximal end of the tibia T. The PSI E-M guide 50 differs fromthe previously described pin guides in that it includes an elongatedrigid alignment rod 52 which extends distally from the upper mountingbody 54, and which has a malleoli clamping element 56 at its distal end.While the alignment rod 52 may be standardized across all, or at least anumber of patient sub-populations, each of the opposed end portions,namely the proximal mounting body 54 and the distal malleoli clampingelement 56, is a PSI component that is purposed designed based on theanatomical features and needs of the individual patient. One of thepossible benefits of the PSI E-M guide 50 is that it permits a lessinvasive surgical procedure (i.e. minimally invasive surgery), becauseno arms having spikes are included for contact with the tibial plateau.Accordingly, less of the bone needs to be accessed for engagement of thePSI E-M guide 50 thereto.

Much as per the PSI tibial pin guide 10 described above, however, thePSI E-M guide 50 is first located relative to the tibia T by an anteriorpin 11 which mates within a corresponding slot 16 formed, in this case,in the proximal body 54 of the PSI E-M guide 50. This pin-slotengagement between the anterior pin 11 and the proximal body 54 of thePSI E-M guide 50 sets, or constrains, the rotation of the device. Theproximal body 54 also includes a posteriorly extending finger 55 whichincludes a visual guide, such as an arrow marking or shape for example,which can be aligned with a known mechanical axis entry point on thetibia T so permit for the verification of the alignment with themechanical axis of the tibia, thereby permitting the V-V alignment ofthe of the PSI E-M guide 50.

A posterior abutting element 58 is disposed behind the proximal body 54of the PSI E-M guide 50, and provides an anchor element which abuts theanterior surface of the tibia T for positioning the component relativethereto. This abutting anchor element 58 is accordingly disposed at alocation on the PSI component which corresponds to a point on the bonewhich is disposed in an area of expected high accuracy on the X-raygenerated digital bone model (namely, along the anterior peripheralcontour of the proximal tibia). The proximal body also includes amedially extending portion 53 having two pin holes 57 extendingtherethrough for receiving, and thus positioning, the pins 31 used tomount the resection cutting guide 30 thereto.

Although the relative orientation of the pins 31 can be varied somewhatwhen using the PSI E-M guide 50, it is otherwise not readily adjustable(e.g. in height, etc). Rather, because both the distal malleoli clamp 56and the proximal body 54 are both PSI components purposed design for theindividual bone, the PSI E-M guide 50 can be designed such as to beaccurately mounted to the tibia T to allow the pins 31 to be insertedthrough the guide holes 57 in their determined position and orientation.

Referring now to FIGS. 9-10, another alternate PSI component of thepresently proposed suite of surgical implements is shown, which couldalternately be used instead of the PSI tibial pin guide 10, the PSI jig40 or the PSI E-M guide 50. In this embodiment, a PSI hip-knee-ankle(HKA) instrument 60 is provided, which can be similarly used toaccurately position the pins 31 to be used to mount the resectioncutting guide 30 to the proximal end of the tibia T. The PSI HKAinstrument 60 includes an elongated rigid alignment rod 52, of fixedlength, which extends distally from an upper mounting body 64 and whichhas a malleoli clamping element 56 at its distal end, much as per thePSI E-M guide 50 described above. Accordingly, the PSI malleoli clampingelement 56 is used to clamp the component onto the malleoli of thepatient, thereby aligning the instrument with the mechanical axis of thetibia.

In contrast to the previously described instruments, however, theproximal end of PSI HKA instrument 60 engages both the tibia and thefemur, as seen in FIGS. 9 and 10. More particularly, the PSI proximalmounting body 64 of the PSI HKA instrument 60 includes both a tibialportion 66 and a femoral portion 68.

The tibial portion 66 is engaged in place relative to the tibia using ananterior pin 11 which is received within a corresponding slot 16, in thesame manner as described above with the previously tibial instruments.This pin-slot engagement between the anterior pin 11 and the slot 16 inthe tibial portion 66 of the PSI proximal body 64 sets, or constrains,the rotation of the device.

A posterior abutting element 70 is disposed behind the tibial portion 66of the PSI proximal body 64, and provides an anchor element which abutsthe anterior surface of the tibia T for positioning the componentrelative thereto. This abutting anchor element 70 is accordinglydisposed at a location on the PSI component which corresponds to a pointon the tibia which is disposed in an area of expected high accuracy onthe X-ray generated digital bone model (namely, along the anteriorperipheral contour of the proximal tibia). The tibial portion 66 of thePSI proximal body 64 also includes a medially extending portion 73having two pin holes 71 extending therethrough for receiving, and thuspositioning, the pins 31 used to mount the resection cutting guide 30 tothe tibia T.

The femoral portion 68 of the PSI proximal mounting body 64 of the PSIHKA instrument 60 is interconnected with the tibial portion 66 by asliding and/or pivoting joint connection which allows for one or more ofrelative P-D and F-E displacement between the two portions 66 and 68,but does not allow for relative angular rotation therebetween. Moreparticularly, the uppermost end of the tibial portion 66 forms a plate72 which is received within a corresponding slot 74 formed in the lowerend of the femoral portion 68. The slot 74 therefore defines two spacedapart flanges 75 between which the plate 72 is received. Two holes 73are provided in each of the flanges 75, and two correspondingly sizedholes (not visible) are also defined through the plate 72. These holesmay be aligned, such that a pivot pin is fed therethrough. Accordingly,without any such pivot pin in place, this joint between the tibial andfemoral portions 66 and 68 allows for relative sliding displacementtherebetween, substantially in the proximal-distal direction. However,when a single pin is disposed through one of the pin holes 73 and thecorresponding hole in the plate 72, a pivoting interconnection betweenthe two portions 66, 68 is thereby formed. This accordingly allows forrelative rotation therebetween in the flexion-extension plane. Further,if a second pin is disposed through the other of the two pin holes 73and the corresponding hole in the plate 72, no further rotation ispermitted between the tibial portion 66 and the femoral portion 68 ofthe PSI proximal mounting body 64. This adjustment mechanism thereforeprovides adjustment flexibility in order to be able to selectivelydisplace (e.g. translate or rotate), or lock, the tibial portion 66 andthe femoral portion 68 of the PSI body 64 with respect to each other.

The femoral portion 68 of the PSI proximal mounting body 64 alsoincludes a pair of pin holes 76 which extend through the body thereofand receive pins 31 therethrough for mounting a resection cutting guideto the femur, once the PSI HKA instrument 60 is positioned in place. Theresection cutting guide may be the same PSI resection cutting guide 30as described above (see FIG. 4), or alternately a different one specificfor the femur. In order to accurate locate the femoral portion 68 of thePSI proximal mounting body 64, it also includes a proximally extendingblade 78 having a femur abutting anchor element 80 thereon. In the samemanner as those previously describe above, the femur abutting anchorelement 80 is also disposed at a location on the PSI component whichcorresponds to a point on the bone (in this case the femur) which isdisposed in an area of expected high accuracy on the X-ray generateddigital bone model (namely, in this case, along the anterior peripheralcontour of the distal femur).

When using the PSI HKA instrument 60, the pins for the tibial resectionare positioned, aligned and fixed in place in the same manner as per thePSI E-M guide 50 described above. However, in order to also correctlylocate the PSI HKA instrument 60 to allow for pins for the femoralresection to be positioned in the desired position and orientation, boththe tibia T and femur F are preferably positioned in the same relativeorientation as when the X-ray scans were taken. Accordingly, in order todo so, a leg alignment jig 82 may be provided, as shown in FIG. 11. Theleg alignment jig 82 is thus configured such as to position the leg ofthe patient, and thus the tibia T and femur F thereof, in asubstantially identical relative position as when the X-ray scans weretaken of the bones. The leg alignment jig 82 therefore allows thesurgeon to set the leg as it was taken during the X-ray, therebyproviding the best positioning for reproducing the planning andtherefore maximizing precision of the operation. While the use of such aleg alignment jig 82 is not necessary, it may be useful to use thisadditional component for the reasons above.

Given that the PSI HKA instrument 60 is also used to locate the pins formounting to the femur, the PSI HKA instrument 60 can also be used inconjunction with the adjustable femoral resection cutting guide 130 ofFIG. 14, and the PSI A-P sizers 210 and 310 of FIGS. 15a and 15 b.

FIG. 12 depicts a final embodiment of a PSI tibial pin guide component,which is a hybrid PSI pin and E-M guide 84. Essentially, this embodimentis a combination of the PSI tibial pin guide 10 and the PSI E-M guide50. However, the PSI pin and E-M guide 84 differs in that it does notuse or require an anterior locating pin 11, as per the devices of theabove-mentioned embodiments. Accordingly, the proximal mounting body 85has bone spikes 86 which form proximal anchor elements that engage thetibial plateau, which set the V-V angular position of the PSI guide 84.Because these anchor elements 86 are offset from each other in theanterior-posterior direction, they also serve to set rotational positionof the PSI guide 84. The distal malleoli ankle clamps (not shown in FIG.12), located at the end of the alignment rod 52, are used to set the F-Eposition. As per the embodiments above, the proximal mounting body 85also includes a medially extending portion 88 through which a pair ofpin holes 87 extend, which are used to guide the pins 31 of theresection cutting guide block 30.

Femoral Components

Much as per the tibial components described above, the present suite ofPSI implement for TKR surgery also include a number of embodiments ofcomponents which can be used for positioning the locating pins 31 on thefemur, which used to mount a resection cutting block, such as theresection cutting guide 30 as described above (FIG. 4) which can also beused to resect the distal femur. Again, these PSI components are alsospecifically designed to be used when the digital bone model of thepatient's femur is generated using only X-ray images.

Referring to FIGS. 13a-13b , a PSI femoral pin guide 110 is shown whichadapted to be mounted to the distal femur and which is produced based onat least two X-rays of the femur, taken from two different angularpositions. The PSI femoral pin guide 110 includes generally a body 112including a proximally extending portion 115 and a pair of posteriorlyextending arms 113. The posteriorly extending arms 113 each have adistal anchor element 114 disposed near the remote ends thereof, the twodistal anchor elements 114 comprising bone spikes or nails which areadapted to piece any cartilage, if necessary, and abut directly on thedistal condylar surfaces of the femur. These distal bone anchors 114accordingly locate, or constrain, the PSI femoral pin guide 110 in theV-V orientation. The proximally extending portion 115 includes ananteriorly extending blade 118 which acts abuts the anterior surface ofthe distal femur and thus serves as another anchor element for locatingthe PSI guide 110. The anteriorly extending blade 118 providesconstraint in the F-E orientation.

Accordingly, the PSI femoral pin guide 110 includes one or more anchorelements disposed at different anchor points. In this case, at leastthree anchor elements are provided, namely the two distal bone spikes114 which abut medially-laterally opposite sides of the distal condylarsurfaces and anteriorly extending blade 118. Each of these anchorelements is disposed at a location on the PSI femoral pin guide 110which corresponds to, or more particularly overlies, points on the bonewhich correspond to areas of expected high accuracy on the X-raygenerated bone model. More particularly, the two distal bone spikes 114are located substantially along a distal bone peripheral contour asdefined in a frontal X-ray image taken of the femur F, and theanteriorly extending blade 118 is located substantially along ananterior bone peripheral contour as defined in a medial or a lateralX-ray image take of the femur F.

The body 112 of the PSI femoral pin guide 110 also includes a pin guideelement 122 disposed in the proximally extending portion 115 of the body112. A pair of pin guide holes 124 extend through the pin guide element122, and are configured to receive therethrough the bone pins 31 whichare used to mount the resection cutting block 30 to the femur.

The PSI femoral pin guide 110 may also include one or more visualalignment guides, including for example an alignment arrow 120 which maybe used to visually align the guide 110 with a known anatomical landmarkand a patient-specific shaped contour 122 (see FIG. 13a ) which isformed on an interior surface of the guide 110 and is visible though thewindow opening 128 defined in the body 112. The PSI contour 122 isspecifically formed such as to correspond to the determined contour ofthe patient's bone on the anterior side of the distal femur, so that thesurgeon can align this PSI contour 122 with the corresponding shape ofthe bone contour, thereby ensuring accurate alignment. Either of thesevisual alignment guides 122 and 128 may be used in order to align thePSI femoral pin guide 110 as required on the femur F.

The body 112 of the PSI femoral pin guide 110 may also include amedially extending arm 127 having a bone abutting element 129 at the endthereof, however this portion of the femur may be less accuratelyreproduced in the X-ray generated bone model, and therefore the mediallyextending arm 130 may be used for additional alignment guidance ratherthan primary location.

The PSI femoral pin guide 110 is designed to be used in conjunction withthe adjustable femoral resection cutting guide 130 of FIG. 14, and thePSI A-P sizers 210 and 310 of FIGS. 15a and 15b , as will be seen.

FIG. 14 depicts an adjustable femoral resection cutting guide 130 whichfunctions much like the resection cutting guide 30 as described above(FIG. 4) with reference to the tibial resection. The femoral resectioncutting guide 130 is particularly adapted to be used in conjunction withthe PSI femoral pin guide 110, which locates the pins in the femur towhich the femoral resection cutting guide 130 is mounted. Similarly tothe cutting guide 30, the femoral resection cutting guide 130 is alsoadjustable such that the portion 132 having the cutting guide slot 137therein can be adjusted in the proximal-distal direction relative to thefixed mounting base 134 so as to be able to adjust at least a resectiondepth.

Referring now to FIG. 15a , a PSI anterior-posterior (A-P) sizer ismounted to the distal end of the femur, and may be used in conjunctionwith both the PSI femoral pin guide 110 and the femoral resectioncutting guide 130 as described above.

The PSI A-P sizer 210 includes a, which sets the rotational positionrelative to the femur F based on the posterior condyles by employing twobone anchors in the form of bone spikes

The PSI A-P sizer 210 includes generally a body 212 which abuts thedistal end of the condyles of the femur F, and includes a pair ofproximally extending arms 213. The posteriorly extending arms 213 eachhave a distal anchor element 214 disposed near the remote ends thereof,the two distal anchor elements 214 comprising bone spikes or nails whichare adapted to piece any cartilage, if necessary, and abut directly onthe posterior condylar surfaces of the distal femur. These bone anchors114 accordingly set, or constrain, the PSI A-P sizer 210 in rotation.

Accordingly, the PSI A-P sizer 210 includes one or more anchor elementsdisposed at different anchor points. In this case, at least two anchorelements are provided, namely the two bone spikes 214 which abutposterior condyles. Each of these anchor elements is disposed at alocation on the PSI A-P sizer 210 which corresponds to, or moreparticularly overlies, points on the bone which correspond to areas ofexpected high accuracy on the X-ray generated bone model. Moreparticularly, the two bone spikes 214 are located substantially along aposterior bone peripheral contour as defined in a medial or lateral sideX-ray image taken of the femur F.

The body 212 of the PSI A-P sizer 210 also includes a pin guide element222 of the body 212. A pair of pin guide holes 224 extend through thepin guide element 222, and are configured to receive therethrough thebone pins which mount a posterior resection cutting block, such as the“4-in-1” cutting guide block 230 as shown in FIG. 15b , to the femur inorder to perform the posterior resection cuts.

The PSI A-P sizer 210 may also include one or more visual alignmentfeatures, including for example the transverse marking lines 220 on thebody 212 which define resection cut line positions and the centralmarking line 226 which defines the trans-epicondylar axis line.

In FIG. 15b , an alternate PSI A-P sizer 310 is shown, which is similarto the PSI A-P sizer 210 but having an additional attachment clip 312for engaging the “4-in-1” posterior cutting guide block 230.

FIG. 15c depicts simply an additional adjustment instrument 350 for usein re-positioning the posterior cutting guide block 230 relative to itsmounting pins and thus relative to the bone. For example, the adjustmentinstrument 350 permit the sliding displacement of the posterior cuttingguide block 230 in the anterior posterior direction and/or rotating theposterior cutting guide block 230 internally or externally.

FIG. 16 shows a PSI femoral pin guide jig 240 in accordance with analternate embodiment of the present disclosure. Much as per the PSItibial pin guide jig 40 of FIG. 6, the PSI femoral pin guide jig 240 maybe alternately used to align and position the mounting pins for thefemoral resection cut guides, however provides less adjustment features.The PSI femoral pin guide jig 240 is more akin to pin placement jigsused in conjunction with MRI-generated digital bone models. Nonetheless,however, the PSI femoral pin guide jig 240 is specifically designed tobe used with digital bone model generated only using X-ray images.Accordingly, the PSI femoral pin guide jig 240 also includes one or moreanchor elements disposed at different anchor points. Two different pairsof pin holes 245 and 247 also extend through the body 244, and are usedas described above to position the pins used to mount the resectioncutting block to the femur. The anchor elements of the PSI femoral pinguide jig 240 which abut the femur are disposed at locations on the PSIcomponent which correspond to, or more particularly overly, points onthe bone which are disposed in areas of expected high accuracy on theX-ray generated digital bone model.

The embodiments of the invention described herein are intended to beexemplary. Those skilled in the art will therefore appreciate that thepresent description is illustrative only, and that various alternativesand modifications can be devised without departing from the scope of thepresent invention.

Accordingly, the present description is intended to embrace all suchalternatives, modifications and variances.

The invention claimed is:
 1. A patient specific system for knee replacement surgery, the patient specific system comprising: a surgical guide adapted to be positioned on a bone; a digital bone model of the bone generated using at least two two-dimensional X-ray scans of the bone taken from different angular positions; and a patient specific instrument for positioning the surgical guide on the bone, the patient specific instrument formed based on the digital bone model, the patient specific instrument including: a body having fastener guide holes, the fastener guide holes adapted to receive fasteners therein used to fasten the surgical guide to the bone; and one or more anchor elements on the body adapted to abut one or more surfaces of the bone, the anchor elements being disposed in locations on the body of the patient specific instrument overlying a peripheral bone contour of the bone in at least one of the two-dimensional X-ray scans, said locations and the peripheral bone contour corresponding to areas of expected high accuracy on the digital bone model generated by the two-dimensional X-ray scans.
 2. The patient specific system of claim 1, wherein the patient specific instrument includes a patient specific pin guide adapted for aligning bone pins on the bone, the bone pins being operable to mount the surgical guide thereto.
 3. The patient specific system of claim 2, wherein the patient specific instrument has at least three of said anchor elements thereon.
 4. The patient specific system of claim 3, wherein the at least three anchor elements include two bone spikes spaced apart in a medial-lateral direction.
 5. The patient specific system of claim 4, wherein the patient specific instrument includes one of a tibial pin guide and a femoral pin guide, the bone spikes of the tibial pin guide being located on a proximal end of the tibial pin guide, and the bone spikes of the femoral pin guide being located on a distal end of the femoral pin guide.
 6. The patient specific system of claim 5, wherein the tibial pin guide includes a distally located jack screw forming one of said anchor elements and adapted to abut an anterior surface of the tibia.
 7. The patient specific system of claim 5, wherein the femoral pin guide includes an anteriorly extending blade on a proximal end thereof, the anteriorly extending blade forming one of said anchor elements and adapted to abut an anterior surface of the femur.
 8. The patient specific system of claim 1, further comprising an extra-medullary guide mounted to the body, the extra-medullary guide including an elongated rigid alignment rod extending distally from the body and having a malleoli clamping element at a distal end thereof.
 9. The patient specific system of claim 1, wherein the one or more anchor elements include a posterior abutting element disposed behind the body of the patient specific instrument, the posterior abutting element forming one of said anchor elements.
 10. The patient specific system of claim 1, further comprising a hip-knee-ankle instrument including a tibia engaging portion and a femur engaging portion, each having a body having a pair of said fastener guide holes extending therethrough and one or more of said anchor elements thereon.
 11. The patient specific system of claim 10, further comprising an extra-medullary guide mounted to the body of the tibia engaging portion, the extra-medullary guide including an elongated rigid alignment rod extending distally from the body and having a malleoli clamping element at a distal end thereof.
 12. The patient specific system of claim 1, wherein the surgical guide is a resection cutting guide.
 13. The patient specific system of claim 1, further comprising a pair of arms extending posteriorly from the body, each of the arms having one of the anchor elements disposed near a remote end thereof, said one of the anchor elements forming a posterior anchor of the patient specific instrument.
 14. The patient specific system of claim 1, wherein the surgical guide and the body of the patient specific instrument are removably attached to each other.
 15. The patient specific system of claim 1, wherein the surgical guide and the patient specific instrument are integrally formed.
 16. The patient specific system of claim 1, further comprising an optical positioning element operable to position the patient specific instrument relative to the bone.
 17. The patient specific system of claim 1, wherein the fastener guide holes comprise a pair of pin guide holes extending through the body.
 18. The patient specific system of claim 1, wherein the two-dimensional X-ray scans are taken from substantially perpendicular positions, said locations on the body of the anchor elements corresponding to points on the peripheral bone contours in at least one of a frontal position and a medial or lateral position.
 19. The patient specific system of claim 1, wherein the patient specific instrument is integrally formed of a material produced by additive manufacturing.
 20. A patient specific instrument for knee replacement surgery, the patient specific instrument comprising: a digital bone model of a bone generated using at least two two-dimensional X-ray scans of the bone taken from different angular positions, the digital bone model including a peripheral bone contour defined in at least one of the X-ray images; an instrument body having fastener guide holes, the fastener guide holes adapted to receive fasteners therein used to fasten the surgical guide to a bone; and one or more anchor elements on the instrument body adapted to abut the bone, the anchor elements being disposed in locations on the instrument body of the patient specific instrument overlying the peripheral bone contour of the digital bone model, said locations on the instrument body corresponding to areas of expected high accuracy on the digital bone model. 